Top insulator for secondary battery and method for manufacturing the same

ABSTRACT

To solve the above problem, a method for manufacturing a top insulator configured to be inserted into a case of a secondary battery, according to an embodiment of the present invention includes: preparing a top insulator fabric by applying a silicone rubber to at least one surface of a glass fiber fabric formed by crossing weft yarns and warp yarns of glass fiber raw yams; and punching the top insulator fabric.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of the priority of KoreanPatent Application Nos. 10-2018-0010900, filed on Jan. 29, 2018, and10-2018-0125530, filed on Oct. 19, 2018, which are hereby incorporatedby reference in their entirety.

TECHNICAL FIELD

The present invention relates to a top insulator for a secondary batteryand a method for manufacturing the same, and more particularly, to a topinsulator for a secondary battery, which is improved in properties suchas heat resistance and chemical resistance and is suppressed ingeneration of dust during punching, and a method for manufacturing thesame.

BACKGROUND ART

In general, secondary batteries include nickel-cadmium batteries,nickel-hydrogen batteries, lithium ion batteries, and lithium ionpolymer batteries. Such a secondary battery is being applied to and usedin small-sized products such as digital cameras, P-DVDs, MP3Ps, mobilephones, PDAs, portable game devices, power tools, E-bikes, and the likeas well as large-sized products requiring high power such as electricvehicles and hybrid vehicles, power storage devices for storing surpluspower or renewable energy, and backup power storage devices.

In general, in order to manufacture the lithium secondary battery,first, electrode active material slurry is applied to a positiveelectrode collector and a negative electrode collector to manufacture apositive electrode and a negative electrode. Then, the electrodes arestacked on both sides of a separator to form an electrode assembly.Also, the electrode assembly is accommodated in a battery case, anelectrolyte is injected, and then, sealing is performed.

Such a secondary battery is classified into a pouch type secondarybattery and a can type secondary battery according to a material of acase accommodating the electrode assembly. In the pouch type secondarybattery, an electrode assembly is accommodated in a pouch made of aflexible polymer material having a variable shape. Also, in the can typesecondary battery, an electrode assembly is accommodated in a case madeof a metal or plastic material having a predetermined shape.

The can type secondary battery is classified into a prismatic typesecondary battery in which the case has a polygonal shape and a cylindertype secondary battery in which the battery case has a cylindrical shapeaccording to the shape of the battery case.

FIG. 1 is a partial cross-sectional view of a cylindrical secondarybattery 2 according to the related art.

In general, as illustrated in FIG. 1 , the cylindrical secondary battery2 includes a cylindrical battery can 12, a jelly-roll type electrodeassembly 13 accommodated in the battery can 12, a cap assembly 11coupled to an upper portion of the battery can 12, a beading part 14disposed on a front end of the battery can 12 to mount the cap assembly11, and a crimping part 15 for sealing the battery can 12.

The cap assembly 11 has a structure in which a top cap 111 sealing anopening of the battery can 12 and forming a positive electrode terminal,a PTC element 112 that interrupts current by increasing resistance whenan internal temperature of the battery increases, a safety vent 113 thatinterrupts current when an internal pressure of the battery increasesdue to abnormal current and exhausts an internal gas, a CID gasket 114electrically separating the safety vent from a CID filter 115 except fora specific portion, and the CID filter 115 to which a positive electrodelead connected to a positive electrode is connected and which interruptscurrent when a high pressure is generated in the battery, aresequentially stacked.

Also, the cap assembly 11 is installed on a beading part 14 of thebattery can 12 in a state of being mounted on a crimping gasket 116.Thus, under normal operation conditions, a positive electrode of theelectrode assembly 13 is electrically connected to the top cap 111 viathe positive electrode lead 131, the CID filter 115, the safety vent113, and the PTC element 112.

An insulator 26 is disposed on each of the upper and lower ends of theelectrode assembly 13. Here, a top insulator 26 disposed on the upperend insulates the electrode assembly 13 from the cap assembly 11, and abottom insulator (not shown) disposed on the lower end insulates theelectrode assembly 13 from a bottom part of the battery can 12.

However, in the case of the cylindrical secondary battery 2 according tothe related art, the top insulator is made of a thermoplastic resin suchas polyethylene or polypropylene, which has insulating property andelectrolyte resistance and is excellent in punching processability.However, the thermoplastic resin has a considerably low melting point of200° C. to 250° C. Also, there is a problem that when an internaltemperature of the secondary battery 2 increases sharply to exceed 250°C., the top insulator 26 is melted to cause short circuit. To solve thisproblem, although a technique of increasing a thickness of the topinsulator 26 has been proposed, there is a problem that capacity andefficiency of the battery are reduced due to a decrease in an internalspace of the secondary battery 2.

In recent years, a technology has been proposed in which the topinsulator 26 is manufactured by applying phenol, which is athermosetting resin, to a glass fiber fabric. However, a melting pointof phenol itself is very low at a temperature of 40° C., and even if itis applied to the glass fiber fabric, there is a problem that a massdecreases by being oxidized into carbon dioxide or carbon monoxide at atemperature of 600° C. Also, when the glass fiber fabric is coated withphenol and then punched in a round disc shape, a large amount of dust isgenerated. Thus, it is difficult to continuously produce the product,resulting in a decrease in production amount and an increase inmanufacturing cost.

DISCLOSURE OF THE INVENTION Technical Problem

To solve a problem to be solved, an object of the present invention isto provide a top insulator for a secondary battery, which is improved inproperties such as heat resistance and chemical resistance and issuppressed in generation of dust during punching, and a method formanufacturing the same.

The objects of the present invention are not limited to theaforementioned object, but other objects not described herein will beclearly understood by those skilled in the art from descriptions below.

Technical Solution

To solve the above problem, a method for manufacturing a top insulatorconfigured to be inserted into a case of a secondary battery, accordingto an embodiment of the present invention includes: preparing a topinsulator fabric by applying a silicone rubber to at least one surfaceof a glass fiber fabric formed by crossing weft yarns and warp yarns ofglass fiber raw yarns; and punching the top insulator fabric.

Also, the preparing the top insulator fabric may include applying firstsilicone rubber, and wherein the applying the first silicone rubber mayinclude: applying a first solution, in which a first silicone polymer isdissolved, to the at least one surface; and drying the applied firstsolution to apply the first silicone rubber.

Also, the preparing the top insulator fabric may further includeapplying second silicone rubber, wherein, after the applying the firstsilicone rubber, the applying the second silicone rubber may include:applying a second solution, in which a second silicone polymer isdissolved, to the at least one surface; and drying the applied secondsolution to apply the second silicone rubber.

Also, the applying the first silicone rubber may be performed so thatthe first silicone rubber is attached to the glass fiber raw yarns, anda pore is formed between the glass fiber raw yarns.

Also, the pore may be a pore formed between the glass fiber raw yarnsthat are perpendicular to each other.

Also, in applying the second silicone rubber, the second silicone rubbermay be inserted into the pore.

Also, the first solution may have a viscosity less than that of thesecond solution.

Also, after the applying the second silicone rubber, the first siliconerubber and the second silicone rubber may be stacked on at least onesurface of the glass fiber fabric.

Also, after the applying the first silicone rubber, the first siliconerubber may be stacked on at least one surface of the glass fiber fabric.

Also, after the preparing the top insulator fabric, the glass fiberfabric and the top insulator fabric may have a same thickness.

Also, in the punching the glass fiber, the glass fiber may be punched tohave a disc shape.

Also, in the preparing the top insulator fabric, the silicone rubber maybe applied to all surfaces of the glass fiber fabric.

To solve the above problem, a top insulator to be inserted into a caseof a secondary battery, according to an embodiment of the presentinvention includes: a glass fiber including crossed weft yarns and warpyarns of raw yarns of the glass fiber; and a silicone rubber on at leastone surface of the glass fiber, wherein the top insulator is heatresistant to a temperature of at least 250° C.

Also, when heated at a temperature of 600° C., a mass loss due topyrolysis of the top insulator may be 10 wt % to 15 wt %.

Also, when heated at a temperature of 950° C., the mass loss of the topinsulator may be 10 wt % to 15 wt %.

Also, when heated at the temperature of 950° C., the mass loss of thetop insulator may be 12 wt % to 14 wt %.

Also, when impregnated into an electrolyte containing 10 wt % or more oflithium bis(fluorosulfonyl)imide (LIFSI) and stored for 1 week or moreat a temperature of 72° C., a reduction amount of lithiumbis(fluorosulfonyl)imide (LIFSI) may be 1 wt % to 3 wt %.

Also, when impregnated into the electrolyte containing 10 wt % or moreof lithium bis(fluorosulfonyl)imide (LIFSI) and stored for 1 week ormore at the temperature of 72° C., the reduction amount of lithiumbis(fluorosulfonyl)imide (LIFSI) may be 1.5 wt % to 2.5 wt %.

Also, when the secondary battery is heated at a temperature of 600° C.or more so as to be exploded, a pinhole may be not formed in the batterycase.

Also, when the top insulator is stretched to both sides, a tensilestrength may be 120 N/mm² to 150 N/mm², and an elongation may be 5% to10%.

Also, when the top insulator is stretched to both sides, the tensilestrength may be 130 N/mm² to 140 N/mm², and the elongation may be 7% to8%.

Particularities of other embodiments are included in the detaileddescription and drawings.

Advantageous Effects

The embodiments of the present invention may have at least the followingeffects.

The silicone rubber may be applied to the glass fiber fabric tomanufacture the top insulator for the secondary battery, therebyimproving the properties such as the heat resistance and the chemicalresistance.

In addition, when the top insulator fabric is punched to manufacture thetop insulator for the secondary battery, the generation of the dust maybe suppressed to enable the products to be continuously produced,increase in production amount, and decrease in manufacturing cost.

Also, the top insulator fabric may have the flexibility and be easilyrolled to easily form the mother roll, and thus, the top insulator forthe secondary battery may be easily manufactured.

The effects of the prevent invention are not limited by theaforementioned description, and thus, more varied effects are involvedin this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a cylindrical secondarybattery according to a related art.

FIG. 2 is a flowchart illustrating a method for manufacturing a topinsulator according to an embodiment of the present invention.

FIG. 3 is a partial cross-sectional view of a cylindrical secondarybattery according to an embodiment of the present invention.

FIG. 4 is a plan view of the top insulator according to an embodiment ofthe present invention.

FIG. 5 is a side view of the top insulator according to an embodiment ofthe present invention.

FIG. 6 is a flowchart illustrating a method for manufacturing a topinsulator according to another embodiment of the present invention.

FIG. 7 is a partial cross-sectional view of a cylindrical secondarybattery according to another embodiment of the present invention.

FIG. 8 is a side view of a top insulator according to another embodimentof the present invention.

FIG. 9 is a partial cross-sectional view of a cylindrical secondarybattery according to further another embodiment of the presentinvention.

FIG. 10 is a schematic view illustrating a state in which first siliconerubber is applied to a glass fiber fabric according to further anotherembodiment of the present invention.

FIG. 11 is a schematic view illustrating a state in which secondsilicone rubber is applied to the glass fiber fabric according tofurther another embodiment of the present invention.

FIG. 12 is a cross-sectional view of a top insulator, taken along lineA-A′ of FIG. 11 according to further another embodiment of the presentinvention.

FIG. 13 is an SEM photograph magnified 1,500 times of the top insulator,which is actually manufactured according to further another embodimentof the present invention.

FIG. 14 is an SEM photograph magnified 1,000 times of the top insulator,which is actually manufactured according to further another embodimentof the present invention.

FIG. 15 is an SEM photograph magnified 200 times of the top insulator,which is actually manufactured according to further another embodimentof the present invention.

FIG. 16 is an SEM photograph magnified 40 times of the top insulator,which is actually manufactured according to further another embodimentof the present invention.

FIG. 17 is a graph illustrating results obtained through a heatresistance test of the top insulator according to Manufacturing Exampleof the present invention.

FIG. 18 is a graph illustrating results obtained through a heatresistance test of the top insulator according to Comparative Example 2.

FIG. 19 is a photograph illustrating a state of each of electrolytesamples after a chemical resistance test.

FIG. 20 is a graph illustrating results of a GC-MS test on each of theelectrolyte samples.

FIG. 21 is a photograph illustrating a disassembled state of a secondarybattery with which a top insulator is assembled according toManufacturing Example of the present invention after a stability test.

FIG. 22 is a photograph illustrating a disassembled state of a secondarybattery with which a top insulator is assembled according to ComparativeExample 1 after the stability test.

FIG. 23 is a photograph illustrating a disassembled state of a secondarybattery with which a top insulator is assembled according to ComparativeExample 2 after the stability test.

MODE FOR CARRYING OUT THE INVENTION

Advantages and features of the present disclosure, and implementationmethods thereof will be clarified through following embodimentsdescribed with reference to the accompanying drawings. The presentinvention may, however be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Further, the present invention is only definedby scopes of claims. Like reference numerals refer to like elementsthroughout.

Unless terms used in the present invention are defined differently, allterms (including technical and scientific terms) used herein have thesame meaning as generally understood by those skilled in the art. Also,unless defined clearly and apparently in the description, the terms asdefined in a commonly used dictionary are not ideally or excessivelyconstrued as having formal meaning.

In the following description, the technical terms are used only forexplaining a specific exemplary embodiment while not limiting thepresent invention. In this specification, the terms of a singular formmay comprise plural forms unless specifically mentioned. The meaning of“comprises” and/or “comprising” does not exclude other componentsbesides a mentioned component.

Hereinafter, preferred embodiments will be described in detail withreference to the accompanying drawings.

FIG. 2 is a flowchart illustrating a method for manufacturing a topinsulator 16 according to an embodiment of the present invention.

The top insulator 16 according to an embodiment of the present inventionis manufactured by applying silicone rubber 162 to a glass fiber fabric161. Thus, properties such as heat resistance and chemical resistancemay be improved. Also, when a top insulator fabric is punched tomanufacture the top insulator 16 for the secondary battery, generationof dust may be suppressed to enable products to be continuouslyproduced, increase in production amount, and decrease in manufacturingcost. Also, the top insulator fabric may have the flexibility and beeasily wounded to easily form a mother roll, and thus, the top insulator16 for the secondary battery may be easily manufactured.

Hereinafter, specific contents of each steps illustrated in theflowchart of FIG. 2 will be described with reference to FIGS. 3 to 5 .

FIG. 3 is a partial cross-sectional view of a cylindrical secondarybattery 1 according to an embodiment of the present invention.

As illustrated in FIG. 3 , the cylindrical secondary battery 1 accordingto an embodiment of the present invention includes a battery can 12, ajelly-roll type electrode assembly 13 accommodated in the battery can12, a cap assembly 11 coupled to an upper portion of the battery can 12,a beading part 14 disposed on a front end of the battery can 12 to mountthe cap assembly 11, and a crimping part 15 for sealing the battery can12. The cylindrical secondary battery 1 may be used as a power sourcefor a mobile phone, a notebook computer, an electric vehicle, and thelike, which stably supplies a constant output.

The battery can 12 may be made of a lightweight conductive metalmaterial such as aluminum, nickel, stainless steel, or an alloy thereof.The battery can 12 may have an opened upper portion and a closed bottomportion that is opposite to the upper portion. An electrolyte togetherwith the electrode assembly 13 may be accommodated in an inner space ofthe battery can 12. Although the battery can 12 has a cylindrical shape,the present invention is not limited thereto. For example, the batterycan 12 may have various shape such as a prismatic shape in addition tothe cylindrical shape.

The electrode assembly 13 may have a stack structure including twoelectrode plates such as a positive electrode plate and a negativeelectrode plate, each of which has a wide plate shape in the form of aroll and a separator disposed between the electrode plates to insulatethe electrode plates from each other or disposed on at a left or rightside of one electrode plate. The stack structure may have variousshapes, for example, may be wound in the form of a jelly roll or bestaked in a shape in which the positive electrode plate and the negativeelectrode plate, each of which has a predetermined size, are stackedwith the separator therebetween. Each of the two electrode plates has astructure in which active material slurry is applied to a metal foil ora mesh-shaped collector including aluminum and copper. The slurry may beusually formed by agitating a granular active material, an auxiliaryconductor, a binder, and a plasticizer with a solvent added. The solventmay be removed in the subsequent process. A non-coating portion on whichthe slurry is not applied may be disposed at a starting end and a distalend of the collector in a direction in which the electrode plate iswound. A pair of leads, which respectively correspond to the electrodeplates, are attached to the non-coating portion. The positive electrodelead 131 attached to an upper end of the electrode assembly 13 may beelectrically connected to the cap assembly 11, and the negativeelectrode lead (not shown) attached to a lower end of the electrodeassembly 13 may be connected to a bottom surface of the battery can 12.However, the present invention is not limited thereto. For example, allthe positive electrode lead 131 and the negative electrode lead may bewithdrawn in a direction of the cap assembly 11.

The top insulator 16 insulating each of the electrode assemblies 13 isdisposed on each of upper and lower ends of the electrode assembly 13.Here, the top insulator 16 disposed on the upper end is disposed betweenthe electrode assembly 13 and the cap assembly 11 to insulate theelectrode assembly 13, and the bottom insulator (not shown) disposed onthe lower end is disposed between the electrode assembly 13 and thebottom part of the battery cab 12 to insulate the electrode assembly 13.As illustrated in FIG. 3 , the insulator 16 according to an embodimentof the present invention may be the top insulator 16 disposed on theupper portion of the electrode assembly, but is not limited thereto. Forexample, the insulator 16 may be a bottom insulator (not shown) disposedon the lower portion of the electrode assembly. The top insulator 16according to an embodiment of the present invention will be describedlater.

A center pin (not shown) that prevents the electrode assembly 13 woundin the form of the jelly roll from being unwound and serves as a movingpath of a gas within the secondary battery 1 may be inserted into acenter of the battery can 12.

The electrolyte filled into the battery can 12 may move lithium ionsgenerated by electrochemical reaction of the electrode plates duringcharging and discharging of the secondary battery 1. The electrolyte mayinclude a non-aqueous organic electrolyte that is a mixture of a lithiumsalt and a high-purity organic solvent or a polymer using a polymerelectrolyte.

The cap assembly 11 may be coupled to an opening formed in the upper endof the battery can 12 to seal the opening of the battery can 12. The capassembly 11 may have various shapes such as a circular shape or aprismatic shape according to the shape of the battery can 12. Accordingto an embodiment, the battery can 12 has the cylindrical shape. In thiscase, the cap assembly 11 may also have a disk shape corresponding tothe shape of the battery can 12.

According to an embodiment of the present invention, the cap assembly 11may have a structure in which a top cap 111 sealing the opening of thebattery can 12 and forming the positive electrode terminal, a safetyvent 113 that interrupts current when an internal pressure of thebattery increases due to abnormal current and exhausts a gas within thebattery, and a current interrupt device to which a positive lead 131connected to the positive electrode of the electrode assembly 13 isconnected and which interrupts current when a high pressure occurs inthe battery are sequentially stacked. Also, the cap assembly 11 isinstalled on a beading part 14 of the battery can 12 in a state of beingmounted on a crimping gasket 116. Thus, under normal operationconditions, a positive electrode of the electrode assembly 13 iselectrically connected to the top cap 111 via the positive electrodelead 131, the current interrupt device, the safety vent 113, and the PTCelement 112.

The top cap 111 is disposed on the uppermost portion of the cap assembly11 in a shape protruding upward to form the positive electrode. Thus,the top cap 111 may be electrically connected to a load or an externaldevice such as a charging device. A gas hole 1111 through which the gasgenerated in the secondary battery 1 is discharged may be formed in thetop cap 111. Thus, when the internal pressure increases due to thegeneration of the gas from the electrode assembly 13 due to overchargingor the like, a CID filter 115 of the current interrupt device and thesafety vent 113 may be ruptured, and thus, the internal gas may bedischarged to the outside through the ruptured portion and the gas hole1111. Thus, the charging and discharging are not performed any more tosecure safety of the secondary battery 1. The top cap 111 may be made ofa metal material such as stainless steel or aluminum.

A portion of the top cap 111 contacting the safety vent 113 may not bespecifically limited in thickness as long as the portion of the top cap111 protects various components of the cap assembly 11 from a pressureapplied from the outside, i.e., may have a thickness of 0.3 mm to 0.5mm. When the thickness of the portion of the top cap 111 is too thin, itmay be difficult to exhibit mechanical rigidity. On the other hand, whenthe thickness of the portion of the top cap 111 is too thick, capacityof the battery may be reduced due to an increase in size and weight whencompared to the same standard.

The safety vent 113 may serve for interrupting the current when theinternal pressure of the battery increases due to the abnormal currentor exhausting the gas and may be made of a metal material. The thicknessof the safety vent 113 may vary according to a material, a structure,and the like thereof. That is, the thickness of the safety vent 113 isnot specifically limited as long as the safety vent 113 discharges thegas while being ruptured when a predetermined high pressure is generatedin the battery. For example, the safety vent 113 may have a thickness of0.2 mm to 0.6 mm.

The current interrupt device (CID) may be disposed between the safetyvent 113 and the electrode assembly 13 to electrically connect theelectrode assembly 13 to the safety vent 113. The current interruptdevice includes a CID filter 115 contacting the safety vent 113 totransmit the current and a CID gasket 114 spatially separating andisolating the CID filter 115 and the safety vent 113 from each other.

Thus, the current generated from the electrode assembly 13 flows intothe safety vent 113 via the positive lead 131 and the CID filter 115 ina normal state so that the secondary battery is discharged. However,when the internal pressure of the secondary battery 1 increases due tothe abnormal current, the internal pressure of the battery may increaseby the gas generated in the secondary battery 1 due to the abnormalcurrent. Thus, the connection between the safety vent 113 and the CIDfilter 115 may be interrupted, or the CID filter 115 may be ruptured.Therefore, the electrical connection between the safety vent 113 and theelectrode assembly 13 may be interrupted to secure the safety.

The cap assembly 11 may further include a positive temperaturecoefficient (PTC) element 112 between the safety vent 113 and the topcap 111. The PTC element 112 may increase battery resistance when theinternal temperature increases to interrupt the current. That is, thePTC element 112 electrically connects the top cap 111 to the safety vent113 in the normal state. However, in the abnormal state, for example,when the temperature abnormally increases, the PTC element 112interrupts the electrical connection between the top cap 111 and thesafety vent 113. The PTC element 112 may also vary in thicknessaccording to the material, the structure, and the like thereof, forexample, may have a thickness of 0.2 mm to 0.4 mm. When the PTC element112 has a thickness greater than 0.4 mm, the internal resistance mayincrease, and also, the battery may increase in size to reduce thebattery capacity when compared to the same standard. On the other hand,when the PTC element 112 has a thickness less than 0.2 mm, it may bedifficult to exhibit the current interrupt effect at a high temperature,and the PTC element 112 may be destroyed by a weak external impact.Thus, the thickness of the PTC element 112 may be appropriatelydetermined within the above-described thickness range in considerationof these points in combination.

Even when the secondary battery 1 including the above-described capassembly 11 is used as a power source for a power tool such as anelectric drill, the secondary battery 1 may instantaneously provide anhigh output and be stable against an external physical impact such asvibration and dropping.

The beading part 14 bent inward from the outside may be formed on theupper portion of the battery can 12. The beading part 14 may allow thecap assembly 11, on which the top cap 111, the PTC element 112, thesafety vent 113, and the current interrupt device are stacked, to bedisposed on an upper end of the battery can 12, thereby preventing theelectrode assembly 13 from moving vertically.

As described above, the cap assembly 11 is installed on the beading part14 of the battery can 12 in the state of being mounted on the crimpinggasket 116. The crimping gasket 116 may have a cylindrical shape withboth opened ends. As illustrated in FIG. 3 , one end of the crimpinggasket 116, which faces the inside of the battery can 12, may beprimarily bent substantially vertically toward a central axis and thensecondarily bent vertically toward the inside of the battery can 12 andbe seated on the beading part 14. Also, the crimping gasket 116 has theother end that initially extends in a direction parallel to the centralaxis. However, when a process of coupling the cap assembly 11 andpressing an outer wall of an upper end of the battery can 12 to form acrimping part 15 is performed later, the crimping gasket 116 may be bentin a direction that is substantially vertical along the shape of thecrimping part 15 to proceed to the central axis. Thus, the crimpinggasket 116 has an inner circumferential surface that is closely attachedto the cap assembly 111 and an outer circumferential surface that isclosely attached to an inner circumferential surface of the battery can12.

FIG. 4 is a plan view of the top insulator 16 according to an embodimentof the present invention.

The top insulator 16 for the secondary battery 1, which is inserted intoa case of the secondary battery 1, according to an embodiment of thepresent invention includes: a disc-shaped glass fiber 161 which isformed by crossing weft yarns and warp yarns of raw yarns of the glassfiber 161; and silicone rubber 162 applied to at least one surface ofthe glass fiber 161. Also, the silicone rubber 162 is stacked on atleast one surface of the glass fiber 161.

The glass fiber 161 is manufactured in a long fiber shape by meltingglass in a platinum furnace and drawing the melted glass through asmall-diameter hole. The glass fiber may have excellent in heatresistance, durability, sound-absorbing properties, electric insulation,rust-proof, and easy processability and thus be mainly used for buildinginsulation materials, air filtering materials, electric insulatingmaterials, and the like. According to an embodiment of the presentinvention, the weft yarns and warp yarns of the raw yarns of the glassfiber 161 may cross each other to prepare a fabric of the glass fiber161, and the silicone rubber 162 is applied to the fabric of the glassfiber 161. It is preferable that a cross-section of one strand of theyarn loosened from the glass fiber 161 has a diameter of approximately 4μm to 15 μm.

The silicone rubber 162 is rubber containing silicon. The siliconerubber may have excellent heat resistance and chemical resistance. Thus,strength and elongation of the silicone rubber may be maintained within10% even after being left for 3 days at a temperature of 250° C., andelasticity of the silicone rubber may also be maintained at atemperature of −45° C. Since electrical characteristics are notsensitive to temperature, the silicone rubber is widely used inelectric, electronic and communication fields requiring the heatresistance. The silicone rubber 162 is prepared by mixing variousmaterials. For example, a silicone polymer such as an organopolysiloxaneis used as a raw material. A silica-based filler, a bulking agent forincreasing a volume, a vulcanizing agent such as organic peroxides, aprocessing material such as a low-molecular-weight silicone oligomer, orvarious property improving agents such as BaO, CaO, MgO, and ZnO may bemixed. Furthermore, in order to increase in flame retardancy, flameretardants such as Al(OH)₃, Mg(OH)₂, and BH₃O₃ may be further contained,or pigments may be further contained to facilitate quality inspectionwith the naked eye. Also, the silicone rubber 162 may be prepared bymixing and heating the above materials, followed by vulcanization anddrying processes. The peroxide such as benzoyl peroxide, dicumylperoxide, and the like may be used for the vulcanization process.

To manufacture the top insulator 16 for the secondary battery accordingto an embodiment of the present invention, first, various materialscontaining the silicone polymer are dissolved in a specific solvent toprepare a solution before being mixed and cured. The solvent ispreferably an organic solvent capable of easily dissolving the abovematerials. For example, the solvent includes toluene, xylene, MEK, andthe like.

The prepared solution has a different viscosity depending on aconcentration at which the silicone polymer is dissolved. Here, if theviscosity is too low, the weft yarns and warp yarns of the glass fiber161 may be loosened, and an effect of coating may not be considerable.On the other hand, if the viscosity is too high, the solution is notpenetrated into a pore 3 between the weft yarns and warp yarns of theglass fiber 161, and the pore 3 may not be filled. The viscosity of thesolution may be selected experimentally as an optimum viscosity.

Also, the prepared solution is applied to the fabric of the glass fiber161 (S201) and then dried (S202). When the solution is applied, thesolution may be sprayed onto the glass fiber 161 by using a spray.However, it is preferable to immerse the glass fiber 161 in a containercontaining the solution. As a result, a large amount of solution may bequickly applied to the fabric of the glass fiber 161. When the solutionis applied and dried, the solvent is evaporated, and the silicone rubber162 is applied to the fabric of the glass fiber 161 to form the topinsulator fabric (S203). Also, the top insulator fabric is punched in aspecific shape, the top insulator 16 according to an embodiment of thepresent invention is manufactured (S204). Here, when the top insulator16 is installed in the cylindrical secondary battery 1, as illustratedin FIG. 4 , the top insulator fabric is preferably punched in a discshape so that the top insulator 16 is easily inserted into the batterycan 12 of the cylindrical secondary battery 1. Thus, the top insulator16 may be manufactured by applying the silicone rubber 162 to the glassfiber 161 having the disc shape as a whole.

FIG. 5 is a side view of the top insulator 16 according to an embodimentof the present invention.

As illustrated in FIG. 5 , the top insulator 16 according to anembodiment of the present invention has a shape in which a plurality oflayers are stacked while the silicone rubber 162 is applied to at leastone surface of the glass fiber 161.

The solution may be applied to only one surface of the fabric of theglass fiber 161. However, according to an embodiment of the presentinvention, the solution may be preferably applied to all both surfacesof the fabric of the glass fiber 161. As a result, the silicone rubber162 may be applied to both surfaces of the glass fiber 161 so that thetop insulator 16 according to an embodiment of the present invention hasthe shape in which the plurality of layers are stacked. Although threelayers are stacked in FIG. 5 , the embodiment of the present inventionis not limited thereto. For example, a separate layer may be furtherprovided between the glass fiber 161 and the silicone rubber 162.

FIG. 6 is a flowchart illustrating a method for manufacturing a topinsulator 16 according to another embodiment of the present invention.

The top insulator 16 according to an embodiment of the present inventionis manufactured by applying silicone rubber 162 to at least one surfaceof a glass fiber 161 once. On the other hand, a top insulator 16 aaccording to another embodiment of the present invention is manufacturedby applying silicone rubber 162 a to at least one surface of a glassfiber 161 a several times.

Hereinafter, specific contents of each steps illustrated in theflowchart of FIG. 6 will be described with reference to FIGS. 7 to 8 .

FIG. 7 is a partial cross-sectional view of a cylindrical secondarybattery 1 a according to another embodiment of the present invention.

Hereinafter, descriptions of a cylindrical secondary battery 1 a and atop insulator 16 a according to another embodiment of the presentinvention, which are duplicated with those of the secondary batteryaccording to the abovementioned embodiment of the present invention willbe omitted. This is for convenience of description and is not intendedto limit the scope of rights.

The top insulator 16 a insulating each of electrode assemblies 13 isdisposed on each of upper and lower ends of the electrode assembly 13.As illustrated in FIG. 7 , the insulator 16 a according to anotherembodiment of the present invention may be the top insulator 16 adisposed on the upper portion of the electrode assembly, but is notlimited thereto. For example, the insulator 16 a may be a bottominsulator (not shown) disposed on the lower portion of the electrodeassembly.

The top insulator 16 a for the secondary battery 1 a, which is insertedinto a case of the secondary battery 1 a, according to anotherembodiment of the present invention includes: a glass fiber 161 a whichis formed by crossing weft yarns and warp yarns of raw yarns of theglass fiber 161 a; and silicone rubber 162 a applied to at least onesurface of the glass fiber 161 a. Also, the silicone rubber 162 aincludes: first silicone rubber 1621 a applied first to at least onesurface of the glass fiber 161 a; and second silicone rubber 1622 aapplied to the first silicone rubber 1621 a. To manufacture the topinsulator 16 a according to another embodiment of the present invention,first, various materials containing the silicone polymer are dissolvedin a specific solvent to prepare first and second solutions before beingmixed and cured.

Particularly, a first silicone polymer is dissolved in a first solventto prepare the first solution, and a second silicone polymer isdissolved in a second solvent to prepare the second solution. Theprepared solutions have different viscosities depending on aconcentration at which the silicone polymer is dissolved. Here, it ispreferable that the first solution has a viscosity greater than that ofthe second solution.

Also, the prepared first solution is applied to at least one surface ofthe fabric of the glass fiber 161 a (S601) and then dried (S602). Thefirst solution may be applied to only one surface of the fabric of theglass fiber 161 a. However, according to another embodiment of thepresent invention, the solution may be preferably applied to all bothsurfaces of the fabric of the glass fiber 161 a. When the first solutionis applied and dried, the first solvent is evaporated, and the firstsilicone rubber 1621 a is applied to the glass fiber 161 a (S603).Thereafter, the prepared second solution is applied to at least onesurface to which the first silicone rubber 1621 is applied (S604) andthen dried (S605). When the second solution is applied and dried, thesecond solvent is evaporated, and the second silicone rubber 1622 a isapplied to the first silicone rubber 1622 a (S606). As a result, a topinsulator fabric is prepared.

Since the first solution has a low viscosity, the first solution may beeasily penetrated into a pore 3 between weft yarns and warp yarns of thefabric of the glass fiber 161 a to fill the pore 3. On the other hand,the second solution has a high viscosity to fix the weft yarns and thewarp yarns of the fabric of the glass fiber 161 a without beingloosened, thereby increasing in holding force. Thus, in the topinsulator 16 a according to another embodiment of the present invention,the silicone rubber 162 a may be better mixed with the glass fiber 161 ato increase in holding force.

The top insulator fabric is punched in a specific shape, the topinsulator 16 a according to another embodiment of the present inventionis manufactured (S607). Here, when the top insulator 16 a is installedin the cylindrical secondary battery 1 a, the top insulator fabric ispreferably punched in a disc shape so that the top insulator 16 a iseasily inserted into a battery can of the cylindrical secondary battery1 a.

FIG. 8 is a side view illustrating the top insulator 16 a according toanother embodiment of the present invention.

As illustrated in FIG. 8 , in the top insulator 16 a according toanother embodiment of the present invention, the first silicone rubber1621 a is stacked on at least one surface of the glass fiber 161 a, andthe second silicone rubber 1622 a is stacked on the first siliconerubber 1621 a. That is, the first and second silicone rubber 1621 a and1622 a are sequentially stacked to form a shape in which a plurality oflayers are stacked.

The first and second solutions may be applied to only one surface of thefabric of the glass fiber 161 a. However, according to anotherembodiment of the present invention, the solutions may be preferablyapplied to all both surfaces of the fabric of the glass fiber 161 a. Asa result, the first and second silicone rubber 1621 a and 1622 a may beapplied to both surfaces of the glass fiber 161 a so that the topinsulator 161 a according to another embodiment of the present inventionhas the shape in which the plurality of layers are stacked.Particularly, since the first silicone rubber 1621 a is applied beforethe second silicone rubber 1622 a is applied, the first silicone rubber1621 a is stacked inside the second silicone rubber 1622 a, and thesecond silicone rubber 1622 a is stacked outside the first siliconerubber 1621 a. Although five layers are stacked in FIG. 8 , thisembodiment of the present invention is not limited thereto. For example,a separate layer may be further provided between the glass fiber 161 aand the silicone rubber 1621 a and 1622 a.

FIG. 9 is a partial cross-sectional view of a cylindrical secondarybattery 1 b according to further another embodiment of the presentinvention.

In the top insulator 16 according to an embodiment of the presentinvention and the top insulator 16 a according to another embodiment ofthe present invention, each of the silicone rubber 162 and 162 a isapplied to at least one surface of each of the glass fiber 161 and 161 ato form the shape in which the plurality of layers are stacked. However,in a top insulator 16 b according to further another embodiment of thepresent invention, silicone rubber 162 b is not stacked on a glass fiber161 b, and thus, the top insulator 16 b has the same thickness as theglass fiber 161 b.

However, a method for manufacturing the top insulator 16 b according tofurther another embodiment of the present invention is similar to themethod for manufacturing the top insulator 16 a according to anotherembodiment, and thus, a specific content of each of steps illustrated inthe flowchart of FIG. 6 will be described again with reference to FIGS.9 to 16 . Hereinafter, descriptions of the cylindrical secondary battery1 b and the top insulator 16 b according to further another embodimentof the present invention, which are duplicated with those of thesecondary battery according to the abovementioned embodiment of thepresent invention will be omitted. This is for convenience ofdescription and is not intended to limit the scope of rights.

The top insulator 16 b for the secondary battery, which is inserted intoa case of the secondary battery, according to further another embodimentof the present invention includes: a glass fiber 161 b which is formedby crossing weft yarns and warp yarns of raw yarns of the glass fiber161 b; and silicone rubber 162 b applied to at least one surface of theglass fiber 161 b. Also, the silicone rubber 162 b includes: firstsilicone rubber 1621 b attached to raw yarns of the glass fiber 161 b;and second silicone rubber 1622 b inserted into a pore 3 formed betweenthe raw yarns of the glass fiber 161 b.

To manufacture the top insulator 16 b according to further anotherembodiment of the present invention, a first solution is applied to atleast one surface of a fabric of the glass fiber 161 b (S601) and thendried (S602). According to further another embodiment of the presentinvention, it is preferable that the first solution is applied to allboth surfaces of the fabric of the glass fiber 161 b.

FIG. 10 is a schematic view illustrating a state in which the firstsilicone rubber 1621 b is applied to the fabric of the glass fiber 161 baccording to further another embodiment of the present invention.

The glass fiber 161 b is formed by crossing the raw yarns of the glassfiber 161 b, and the pore 3 is formed between the raw yarns of the glassfiber 161 b that are perpendicular to each other. Here, the firstsolution has a viscosity less than that of the second solution and alsois further less than that of the first solution according to anotherembodiment of the present invention. Thus, the first solution may adhereto only surrounds of the raw yarns of the glass fiber 161 b forming thefabric of the glass fiber 161 b.

After the first solution is applied, the fabric of the glass fiber 161 bis scraped off with a knife or the like. Thus, the fabric of the glassfiber 161 b may be adjusted in thickness. Also, a surface of the fabricof the glass fiber 161 b may be smoothed. Also, when the first solutionis dried (S602), a first solvent is evaporated. As illustrated in FIG.10 , the first silicone rubber 1621 b is applied to the fabric of theglass fiber 161 b (S603). Here, according to further another embodimentof the present invention, since the first silicone rubber 1621 b isclosely attached to adhere to only the raw yarns of the glass fiber 161b, the pore 3 is formed between the raw yarns of the glass fiber 161 b,which are perpendicular to each other.

FIG. 11 is a schematic view illustrating a state in which the secondsilicone rubber 1622 b is applied to the fabric of the glass fiber 161 baccording to further another embodiment of the present invention.

Thereafter, the second solution is applied to at least one surface ofthe fabric of the glass fiber 161 b (S604) and then dried (S605). Here,the second solution has the viscosity greater than that of the firstsolution but less than that of the second solution according to anotherembodiment of the present invention. Thus, the second solution isinserted into the pore 3 formed between the raw yarns of the glass fiber161 b.

After the second solution is applied, the fabric of the glass fiber 161b is scraped off again with a knife or the like. Thus, the fabric of theglass fiber 161 b may be adjusted in thickness. Also, a surface of thefabric of the glass fiber 161 b may be smoothed. Also, when the secondsolution is dried (S605), a second solvent is evaporated. As illustratedin FIG. 11 , the second silicone rubber 1622 b is applied to the fabricof the glass fiber 161 b (S606). Here, according to further anotherembodiment of the present invention, the second silicone rubber 1622 bis inserted into the pore 3 formed between the raw yarns of the glassfiber 161 b, which are perpendicular to each other to fill the pore 3.As a result, a top insulator fabric is prepared.

The top insulator fabric is punched in a specific shape, the topinsulator 16 b according to further another embodiment of the presentinvention is manufactured (S607). Here, when the top insulator 16 b isinstalled in the cylindrical secondary battery 1 b, the top insulatorfabric is preferably punched in a disc shape so that the top insulator16 b is easily inserted into the battery can 12 of the cylindricalsecondary battery 1 b.

FIG. 12 is a cross-sectional view of the top insulator 16 b, taken alongline A-A′ of FIG. 11 according to further another embodiment of thepresent invention.

In the top insulator 16 b according to further another embodiment of thepresent invention, as illustrated in FIG. 12 , the first and secondsilicone rubber 162 b are not formed as separate layers. That is, thefirst silicone rubber 1621 b is closely attached to adhere to only theraw yarns of the glass fiber 161 b, and the second silicone rubber 1622b is inserted into the pore 3 formed between the raw yarns of the glassfiber 161 b. Thus, since the first and second silicone rubber 162 b arenot formed as separate layers, the completed top insulator 16 b has athickness that is equal to or similar to that of the glass fiber 161 bto which the silicone rubber 162 b is not applied.

As described above, the top insulator 16 b insulating each of theelectrode assemblies 13 is disposed on each of upper and lower ends ofthe electrode assembly 13. As illustrated in FIG. 9 , the insulator 16 baccording to an embodiment of the present invention may be the topinsulator 16 b disposed on the upper portion of the electrode assembly,but is not limited thereto. For example, the insulator 16 may be abottom insulator (not shown) disposed on the lower portion of theelectrode assembly.

When the top insulator 16 b according to further another embodiment ofthe present invention is used as the top insulator 16 b, properties suchas heat resistance and chemical resistance may be improved to securethermal and chemical stability. On the other hand, when the insulator 16b is used as the bottom insulator, the thermal and chemical stabilitymay be secured, and also, a heat transfer path through which heat isspread from a lower portion of the electrode assembly 13 may be blocked.According to the related art, the bottom separator may be lost by heatspread through a negative electrode tab of the electrode assembly 13 tocause edge short at a lower portion of the electrode assembly 13.However, the insulator 16 b according to further another embodiment ofthe present invention may be used as the bottom insulator to block theheat transfer path through which the heat is spread to the lower portionof the electrode assembly 13, thereby preventing the edge short at thelower portion of the electrode assembly 13.

FIG. 13 is an SEM photograph magnified 1,500 times of the top insulator16 b, which is actually manufactured according to further anotherembodiment of the present invention, FIG. 14 is an SEM photographmagnified 1,000 times of the top insulator 16 b, which is actuallymanufactured according to further another embodiment of the presentinvention, FIG. 15 is an SEM photograph magnified 200 times of the topinsulator 16 b, which is actually manufactured according to furtheranother embodiment of the present invention, and FIG. 16 is an SEMphotograph magnified 40 times of the top insulator 16 b, which isactually manufactured according to further another embodiment of thepresent invention.

In FIGS. 13 and 14 , the large rounded shapes are the cross-sections ofthe raw yarns of the glass fibers 161 b, and the materials attachedaround the raw yarns of the glass fibers 161 b are the silicone rubber162 b.

As illustrated in FIGS. 13 and 14 , the first silicone rubber 1621 b areclosely attached to adhere between the raw yarns of the glass fiber 161b. Also, as illustrated in FIGS. and 16, the silicone rubber 162 b isnot formed as a separate layer.

In FIGS. 13 to 16 , the pore 3 between the raw yarns of the glass fiber161 b and a state in which the second silicone rubber 1622 b is insertedinto the pore 3 were not photographed. However, it is determined thatthe second silicone rubber 1622 b is inserted into the pore 3 whenconsidering that the silicone rubber 162 b does not form a separatelayer even though the second silicone rubber 1622 b is applied to theglass fiber 161 b.

After the top insulator 16 b according to further another embodiment ofthe present invention is actually manufactured, a composition ratio ismeasured as follows.

TABLE 1 Material name Composition ratio (wt %) Glass Fiber (Fabric)70~80 Siloxanes and silicones, di-Me, 10~15 vinyl group-terminatedDimethylvinylated and trimethylated 0~5 silica Aluminum trihydroxide10~15 Titanium dioxide 0~5

Table 1 shows the composition ratio of the top insulator according toManufacturing Example.

As shown in Table 1, the glass fiber has a composition ratio of 70 wt %to 80 wt %, and the silicone rubber has a composition ratio of 20 wt %to 30 wt %. Particularly, as main chains of a silicone polymer, contentsof siloxanes and silicones, di-Me, and vinyl group-terminated are 10 wt% to 15 wt %, and contents of dimethylvinylated and trimethylated silicaare 0 wt % to 5 wt %. That is, the total composition ratio of thesilicone polymer is 10 wt % to 20 wt %. Also, a content of aluminumtrihydroxide that is a flame retardant is 10 wt % to 15 wt %, and acontent of titanium dioxide that is a pigment is 0 wt % to 5 wt %. Thatis, since dimethylvinylated and trimethylated silica and titaniumdioxide have a minimum value of 0 wt %, it does not need to be containedat all.

The top insulator for the secondary battery, which is inserted into thecase of the secondary battery, according to an embodiment of the presentinvention includes: a glass fiber which is formed by crossing weft yarnsand warp yarns of raw yarns of the glass fiber; and silicone rubberapplied to at least one surface of the glass fiber.

When the top insulator for the secondary battery is heated to atemperature of 600° C. or more, or even 950° C. or more, a mass loss dueto pyrolysis may be 10 wt % to 15 wt %, preferably 12 wt % to 14 wt %.Thus, the top insulator for the secondary battery according to anembodiment of the present invention is excellent in heat resistance.

Also, the top insulator for the secondary battery is impregnated into anelectrolyte containing 10 wt % or more of lithiumbis(fluorosulfonyl)imide (LIFSI) and stored for 1 week or more at atemperature of 72° C., a reduction amount of lithiumbis(fluorosulfonyl)imide (LIFSI) may be 1 wt % to 3 wt %, preferably,1.5 wt % to 2.5 wt %. Thus, the top insulator for the secondary batteryaccording to an embodiment of the present invention is excellent inchemical resistance.

Also, when the secondary battery is manufactured using the top insulatorfor the secondary battery according to an embodiment of the presentinvention, pinholes may not be formed in the battery case when thesecondary battery is heated at a temperature of 600° C. or more and thusexploded. Thus, the top insulator for the secondary battery according toan embodiment of the present invention is excellent in safety.

Also, when the top insulator for the secondary battery according to anembodiment of the present invention is stretched to both sides, tensilestrength may be 120 N/mm² to 150 N/mm², preferably, 130 N/mm² to 140N/mm², and elongation may be 5% to 10%, preferably, 7% to 8%. Thus, thetop insulator for the secondary battery according to an embodiment ofthe present invention is excellent in tensile strength and elongation.

Manufacturing Example

A glass fiber fabric having a width of 1,040 mm, a length of 300,000 mm,and a thickness of 0.3 mm was prepared. Also, 12 kg of siloxanes andsilicones, di-Me, and vinyl group-terminated and 4 kg ofdimethylvinylated and trimethylated silica were added as main chains ofa silicone polymer into 20 kg of a toluene solvent, and 13 kg ofaluminum trihydroxide was added as a flame retardant. In addition, 3 kgof titanium dioxide was further added as a pigment to prepare 52 kg of afirst solution.

After rollers are disposed on both sides of the glass fiber fabric, aknife was disposed on an upper end of each of the rollers. Also, thefirst solution was contained in a container, and the roller rotated toimmerse the glass fiber fabric into the first solution. While therollers reversely rotate to take off the glass fiber fabric, the firstsolution remaining on a surface of the glass fiber fabric was scrapedoff by the knife. Also, the glass fiber fabric was inserted into adrying furnace, and the first solution was dried at a temperature of170° C. for 5 minutes.

Then, 12 kg of siloxanes and silicones, di-Me, and vinylgroup-terminated and 4 kg of dimethylvinylated and trimethylated silicawere added as the main chains of the silicone polymer into 10 kg of atoluene solvent, and 13 kg of aluminum trihydroxide was added as theflame retardant. In addition, 3 kg of titanium dioxide was further addedas a pigment to prepare 41 kg of a second solution.

After rollers are disposed on both sides of the glass fiber fabric, aknife was disposed on an upper end of each of the rollers. Also, thesecond solution was contained in a container, and the roller rotated toimmerse the glass fiber fabric into the second solution. While therollers reversely rotate to take off the glass fiber fabric, the secondsolution remaining on a surface of the glass fiber fabric was scrapedoff by the knife. Also, the glass fiber fabric was inserted into adrying furnace, and the second solution was dried at a temperature of170° C. for 5 minutes.

When the top insulator fabric is prepared as described above, a punchingmachine was inserted to punch the top insulator fabric in a disc shapehaving a diameter of 20 mm to prepare a top insulator according toManufacturing Example.

Comparative Example 1

PET having a nonwoven fabric with a width of 30 mm, a length of 30 mm,and a thickness of 0.3 mm was prepared by using a PET raw materialthrough an electrospinning method.

When the top insulator fabric is prepared as described above, a punchingmachine was inserted to punch the top insulator fabric in a disc shapehaving a diameter of 20 mm to prepare a top insulator according toComparative Example 1.

Comparative Example 2

A glass fiber fabric having a width of 270 mm, a length of 270 mm, and athickness of 0.3 mm was prepared. Also, 5 kg of a phenolic resin and 5kg of aluminum trihydroxide were added to 10 kg of a toluene solvent toprepare 20 kg of a solution.

Three sheets of impregnated fabric were stacked, and heat and pressurewere applied by using a hot press to prepare a cured phenolic topinsulator.

When the top insulator fabric is prepared as described above, punchingequipment was inserted to punch the top insulator fabric in a disc shapehaving a diameter of 20 mm to prepare a top insulator according toComparative Example 2.

Method for Measuring Physical Property

1. Heat Resistance

Each of the top insulators according to foregoing Manufacturing Example,Comparative Example 1, and Comparative Example 2 was inserted into aheat resistance tester (model: TGA Q500) manufactured by TA InstrumentsCo., and heat was gradually applied at a temperature of 25° C. to 950°C. and a temperature increase rate of 10° C./min. Also, a mass of eachtop insulator was measured in real time, and an amount of mass loss dueto pyrolysis was confirmed.

2. Chemical Resistance

Salts and additives were are mixed with a solvent to prepare anelectrolyte. The solvent was prepared by mixing ethylene carbonate (EC),dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) with eachother, and lithium hexafluorophosphate (LiFF6) and lithiumbis(fluorosulfonyl)imide as the salts and various additives were mixed.

Each of the top insulators according to Manufacturing Example,Comparative Example 1, and Comparative Example 2 was impregnated intothe prepared electrolyte and stored at a temperature of 72° C. for 1week. Also, after removing the respective top insulators, theelectrolyte samples were injected into NMR equipment (manufactured byVarian, model name EQC-0279) and GC-MS equipment (manufactured bySHIMADZU, model GC2010 Plus/QP2020, EQC-0291) to perform NMR and GCanalysis, thereby analyzing a composition ratio and reaction byproductsof respective electrolyte samples.

3. Flame Propagation

In this test, the top insulators according to Comparative Examples 1 and2 were not tested, and only the top insulator according to ManufacturingExample was tested. Thus, it was confirmed that the top insulatoraccording to Manufacturing Example satisfies a flame propagationperformance standard. The test standard depends on IMO RESOLUTIONMSC.307 (88).

Particularly, the top insulator according to Manufacturing Example wasinstalled in equipment having a main heat source and an auxiliary heatsource, and flame was applied. Flame as the main heat source isgenerated by using a methane gas having a purity of 99.99% as a fuel ina radiation plate having a width of 483 mm and a length of 284 mm. Here,an amount of heat is 50.5 kW/m² at a point of 50 mm and 23.9 kW/m² at apoint of 350 mm. Also, pilot flame as the auxiliary heat source has alength of about 230 mm, and the flame is generated by using a propanegas as a fuel.

First, in order to standardize the operating conditions of theequipment, a calibration test piece was installed, the radiation plateand the pilot flame were ignited, and it was confirmed that a chimneysignal value is continuously stabilized for at least 180 seconds. Whenthe signal value became stable, the calibration test piece was removed,and the top insulator according to Manufacturing Example was installedwithin 10 seconds. Also, the chimney signal value was continuouslymeasured, and each of a time at which a flame tip reaches a point of 50mm of the top insulator according to Manufacturing Example and a pointat which the flame is extinguished and a time at which the flame isextinguished was recorded.

If no ignition occurs for 600 seconds after the start of the test, or180 seconds elapses after the flame has extinguished, the top insulatoraccording to Manufacturing Example was removed, and a standard testpiece was installed again. The total three top insulators according toManufacturing Example were manufactured, and this process was repeatedthree times in total.

4. Stability

The secondary batteries were manufactured by using the top insulatorsaccording to Manufacturing Example, Comparative Example 1, andComparative Example 2 and then fully charged. Also, when the secondarybatteries are put in the heating furnace maintained at a temperature of600° C. and heated for 3 minutes to 5 minutes, the secondary batteriesare exploded. Also, the exploded secondary batteries were cooled at roomtemperature, and then the cap assembly was disassembled to confirmwhether pinholes occur at the upper edge of the battery can.

5. Tensile Strength and Elongation

Each of the top insulators manufactured according to ManufacturingExample, Comparative Example 1, and Comparative Example 2 was fixed toupper and lower jigs of an universal testing machine (UTM, Model 3340)manufactured by Instron. Also, required force was measured while beingstretched at a speed of 300 mm/min, and this force was evaluated as thetensile strength. Also, a ratio of the stretched length by the tensilestrength was evaluated as the elongation. The test was performed twice,and an average value of respective results was calculated.

Physical Property Measurement Result

1. Heat Resistance

TABLE 2 Temperature range 0~320° C. 320~600° C. 600~700° C. ResidueManufacturing 3.8 wt %  9.3 wt % 0.3 wt % 86.6 wt % Example Comparative—  100 wt % —   0 wt % Example 1 Comparative 40.5 wt % — 59.5 wt %Example 2

FIG. 17 is a graph illustrating results obtained through the heatresistance test of the top insulator according to Manufacturing Exampleof the present invention, and FIG. 18 is a graph illustrating resultsobtained through the heat resistance test of the top insulator accordingto Comparative Example 2. Also, Table 2 shows an amount of mass loss anda residual mass of each top insulator according to a temperature range.

As illustrated in FIG. 17 , the top insulator according to ManufacturingExample decreased gradually in stages. Also, the reduced mass width isshown in Table 2 above. As shown in Table 2, it was confirmed that thetop insulator according to Manufacturing Example has a mass loss of 3.8wt % in the range of 0° C. to 320° C., a mass loss of 9.3 wt % in therange of 320° C. to 600° C., and a mass loss of 0.3 wt % in the range of600° C. to 700° C.

On the other hand, as illustrated in FIG. 18 , a mass of the topinsulator according to Comparative Example 2 continuously decreased upto a temperature of 600° C., and a mass of the top insulator rapidlydecreased in the range of 320° C. to 600° C. As shown in Table 2, it wasconfirmed that the top insulator according to Comparative Example 2 hasa mass loss of 40.5 wt % in the range of 0° C. to 600° C.

When the top insulator according to Comparative Example 1 has atemperature of 600° C., it was completely burned and lost a mass of 100wt %, and it was not shown in the graph because it burned quickly.

Thus, it was confirmed that the top insulator according to ManufacturingExample has the least amount of mass loss of 13.4 wt % due to thepyrolysis at a temperature of 600° C. or more, and even has heatstability up to a temperature of 950° C.

2. Chemical Resistance

TABLE 3 Remaining LiPF6 LiFSI component Ref. 9.5 11.4 79.1 Manufacturing6.5 9.3 84.2 Example Comparative 9.4 11.1 79.5 Example 1 Comparative 7.80.8 91.4 Example 2

FIG. 19 is a photograph illustrating a state of each of the electrolytesamples after the chemical resistance test, and FIG. 20 is a graphillustrating results of a GC-MS test on each of the electrolyte samples.Also, Table 3 shows a composition ratio of the components of eachelectrolyte sample.

As shown in Table 3, LiPF6 and LiFSI relatively decrease in all thesamples, and the remaining components tend to relatively increase.However, this does not mean that LiPF6 and LiFSI are decomposed andchanged into the remaining components of the electrolyte because theabsolute mass is not changed. Since the numerical values shown in Table3 are relative mass ratios, it means that LiPF6 and LiFSI are relativelymore decomposed.

As shown in Table 3, in the top insulator according to ManufacturingExample of the present invention, LiPF6 was reduced by 3 wt %, and LiFSIwas reduced by 2.1 wt % when compared to the Ref. electrolyte. However,in the top insulator according to Comparative Example 1, LiPF6 and LiFSIwere reduced by 0.1 wt % and 0.3 wt %, respectively, and in the topinsulator according to Comparative Example 2, LiPF6 was reduced by 1.7wt %, and LiFSI was reduced by 10.6 wt %. That is, it is seen that LiFSIis the most reduced in the top insulator according to ComparativeExample 2, which indicates that the top insulator according toComparative Example 2 is the most active.

Referring to the photograph of FIG. 19 , it is visually confirmed that acolor of the electrolyte contained in the top insulator according toComparative Example 2 is most changed. Also, in the graph of FIG. 20 ,it is confirmed that the top insulator according to Comparative Example2 has the weakest chemical resistance because a large number ofbyproducts, which are not initially present in the electrolytecontaining the top insulator according to Comparative Example 2, aredetected.

Thus, it was confirmed that the top insulator according to ManufacturingExample is more excellent in chemical resistance than the top insulatoraccording to Comparative Example 2.

However, the top insulator according to Comparative Example 1 had thehighest chemical resistance. However, in the heat resistance test, itwas confirmed that the top insulator according to Comparative Example 1has the lowest heat resistance, and thus, the top insulator according toManufacturing Example is excellent in heat resistance and chemicalresistance.

3. Flame Propagation

TABLE 4 Specimen Manufacturing Manufacturing Manufacturing numberExample 1 Example 2 Example 3 Average Reference Average — — — — ≥1.5combustion sustained heat (MJ/m²) Critical 48.7 49.1 47.9 48.6 ≥20.0flux when extinguished (kW/m²) Total heat 0.01 0.06 0.02 0.03 ≤0.7emission (MJ) Maximum 0.01 0.33 0.29 0.21 ≤4.0 heat release rate (kW)Flame drop None None None None None

TABLE 5 Specimen number Manufacturing Manufacturing ManufacturingExample 1 Example 2 Example 3 Average Average Average combustioncombustion combustion Measurement Elapse time sustained heat Elapse timesustained heat Elapse time sustained heat item (Minute:Second) (MJ/m²)(Minute:Second) (MJ/m²) (Minute:Second) (MJ/m²) Flame reaching 50 00:160.81 00:14 0.71 00:15 0.76 distance (mm) 100 00:28 1.39 00:20 0.99 00:211.04 150 — — — — — — Ignition time 00:13 00:12 00:13 (Minute:Second)Extinguishment 00:54 00:31 00:50 time (Minute:Second) Test time 10:0010:00 10:00 (Minute:Second)

Table 4 shows results of the critical flux at extinguishment, the totalheat emission, the maximum heat release rate, and whether flame dropswith respect to the top insulator according to Manufacturing Example,and Table 5 shows results of the average combustion sustained heat withrespect to the top insulator according to Manufacturing Example.

The combustion sustained heat is a value obtained by multiplying a timefrom first exposure of the specimen to a time at which a flame tipreaches each point by a radiant heat flux irradiated to correspond tothe incombustible calibration plate at the same point. Also, the averagecombustion sustained heat is an average value of the characteristicvalues measured at different locations by the combustion sustained heat.As shown in Table 5, the average combustion sustained heat of the topinsulator according to Manufacturing Example was less than 1.5 that isreference value when the flame reaching distance is 50 mm or 100 mm.

However, in the top insulators according to Manufacturing Examples 1 to3, the ignition started at 13 seconds, 12 seconds, and 13 seconds,respectively. However, the flame was respectively extinguished at 54seconds, 31 seconds, and 50 seconds, and then the top insulators were nolonger ignited. Thus, it was confirmed that the flame is not sustainedin the top insulator because the flame is extinguished at a short timeeven though the average combustion sustained heat is low during thecombustion. That is, it was confirmed that the flame is not easilypropagated to the surroundings thereof to secure safety.

Critical flux at extinguishment means a flow rate of heat at a positionwhere the flame is propagated farthest from a central line of theburning specimen so as to be stopped. The recorded heat flux is obtainedthrough the calibration test of the test machine by using thecalibration plate. As shown in Table 4, the average value of thecritical flux at the extinguishment of the top insulator according toManufacturing Example is 48.6 kW/m², which is larger than the referencevalue of 20.0 kW/m² and thus satisfies the criterion.

The total heat emission means the total heat emission during the testperiod, and the maximum heat release rate means the maximum heat releaserate during the test period. As shown in Table 4, the average value ofthe total heat emission of the top insulator according to ManufacturingExample is 0.03 MJ, which is less than 0.7 MJ that is a reference value,and the average value of the maximum heat release rate is 0.21 kW, whichis less than 4.0 kW that is a reference value.

4. Stability

TABLE 6 Number of Rate of Total pinhole pinhole Number occurrenceoccurrence Manufacturing 41 0  0% Example Comparative 15 3 20% Example 1Comparative 15 0  0% Example 2

FIG. 21 is a photograph illustrating a disassembled state of thesecondary battery with which the top insulator is assembled according toManufacturing Example of the present invention after the stability test,FIG. 22 is a photograph illustrating a disassembled state of thesecondary battery with which the top insulator is assembled according toComparative Example 1 after the stability test, and FIG. 23 is aphotograph illustrating a disassembled state of the secondary batterywith which the top insulator is assembled according to ComparativeExample 2 after the stability test. Also, Table 6 shows the number ofpin hole occurrences and a ratio of the respective top insulators.

As illustrated in FIG. 22 , the pinholes were generated in the secondarybattery in which the top insulator according to Comparative Example 1 isassembled. Particularly, as show in Table 6, among the fifteen secondarybatteries assembled with the top insulator according to ComparativeExample 1, pinholes were generated in three secondary batteries.

On the other hand, as illustrated in FIGS. 21 and 23 , it was confirmedthat the top insulator according to Manufacturing Example and the topinsulator according to Comparative Example 2 did not generate thepinholes at all and had the best stability against the explosion of thebattery.

However, since the top insulator according to Comparative Example 2 isvulnerable in heat resistant, chemical resistance, and stability ratherthan the top insulator according to Manufacturing Example, it wasconfirmed that the top insulator according to Manufacturing Example isexcellent in all heat resistance, chemical resistance and stability.

5. Tensile Strength and Elongation

TABLE 7 Tensile strength (N/mm²) Elongation (%) 1 2 Average 1 2 AverageManufacturing 130.12 137.16 133.64 6.89 7.37 7.13 Example Comparative60.3 53.4 56.9 47.0 51.0 49.0 Example 1 Comparative — — — 0 0 0 Example2

Table 7 shows the tensile strength and elongation of the respective topinsulator.

As shown in Table 7, the top insulator according to ManufacturingExample was broken at an average tensile strength of 133.64 N/mm². Also,an average value of the elongation at this time was 7.13%.

However, the top insulator according to Comparative Example 1 was brokenat an average tensile strength of 56.9 N/mm². Also, an average value ofthe elongation at this time was 49.0%.

Also, the top insulator according to Comparative Example 2 was notstretched at all up to 1000N which is a maximum allowable weight of theuniversal testing machine. Thus, the tensile strength was not measured,and an average value of the elongation was 0%.

Thus, the top insulator according to Comparative Example 1 has a problemof being easily deformed by small force because of low tensile strengthand high elongation. Also, since the top insulator according toComparative Example 2 does not have a stretching property, it may not bemanufactured into a roll type. Thus, since the top insulator is not putinto a line, continuous production may be impossible, and a productionrate may be lowered. However, the top insulator according toManufacturing Example may be manufactured into the roll type in whichthe top insulator is rolled up to one side because of its high tensilestrength and low elongation, and the ability to be stretched to someextent.

As described above, when the glass fiber 161 is coated with the siliconerubber 162, the properties such as the heat resistance and the chemicalresistance may be improved by manufacturing the top insulator 16 for thesecondary battery as compared to the case of coating with athermoplastic resin or phenol according to the related art.Particularly, the phenol has a chain bonding form in which a centralelement is carbon (C), but the silicone polymer as a main raw materialof the silicone rubber 162 has a chain bonding form in which the centralelement is silicone. Accordingly, high thermal stability may beobtained. In addition, when the top insulator 16 for the secondarybattery is punched, the generation of the dust may be suppressed toenable the products to be continuously produced, increase in productionamount, and decrease in manufacturing cost. Furthermore, before the topinsulator 16 for the secondary battery is punched, the top insulatorfabric may have the flexibility and be easily rolled to easily form amother roll, and thus, the top insulator 16 for the secondary batterymay be easily manufactured.

Those with ordinary skill in the technical field of the presentinvention pertains will be understood that the present invention can becarried out in other specific forms without changing the technical ideaor essential features. Therefore, the above-disclosed embodiments are tobe considered illustrative and not restrictive. Accordingly, the scopeof the present invention is defined by the appended claims rather thanthe foregoing description and the exemplary embodiments describedtherein. Various modifications made within the meaning of an equivalentof the claims of the invention and within the claims are to be regardedto be in the scope of the present invention.

The invention claimed is:
 1. A method for manufacturing a top insulatorconfigured to be inserted into a case of a secondary battery, the methodcomprising: preparing a top insulator fabric by applying a siliconerubber to at least one surface of a glass fiber fabric formed bycrossing weft yarns and warp yarns of glass fiber raw yarns; andpunching the top insulator fabric, wherein the preparing the topinsulator fabric comprises applying a first silicone rubber and applyinga second silicone rubber, wherein the applying the first silicone rubbercomprises: applying a first solution, in which a first silicone polymeris dissolved, to the at least one surface; and drying the applied firstsolution to apply the first silicone rubber, wherein, after the applyingthe first silicone rubber, the applying the second silicone rubbercomprises: applying a second solution, in which a second siliconepolymer is dissolved, to the at least one surface; and drying theapplied second solution to apply the second silicone rubber, wherein thefirst solution has a viscosity less than that of the second solution,wherein the applying the first silicone rubber is performed so that thefirst silicone rubber is attached to the glass fiber raw yarns, and apore is formed between the glass fiber raw yarns having the firstsilicone rubber attached thereto, and wherein, in applying the secondsilicone rubber, the second silicone rubber is inserted into the pore tofill the pore.
 2. The method of claim 1, wherein the pore is a poreformed between the glass fiber raw yarns that are perpendicular to eachother.
 3. The method of claim 1, wherein, after the applying the secondsilicone rubber, the first silicone rubber and the second siliconerubber are stacked on the at least one surface of the glass fiberfabric.
 4. The method of claim 1, wherein, after the applying the firstsilicone rubber, the first silicone rubber is stacked on the at leastone surface of the glass fiber fabric.
 5. The method of claim 1,wherein, after the preparing the top insulator fabric, the glass fiberfabric and the top insulator fabric have a same thickness.
 6. The methodof claim 1, wherein, in the punching the glass fiber, the glass fiber ispunched to have a disc shape.
 7. The method of claim 1, wherein, in thepreparing the top insulator fabric, the silicone rubber is applied toall surfaces of the glass fiber fabric.
 8. The method of claim 1,wherein the applying the first silicone rubber further comprises,scraping off the first solution remaining on the surface of the glassfiber fabric with a knife after applying the first solution but beforedrying the applied first solution, and wherein the applying the secondsilicone rubber further comprises scraping off the second solutionremaining on the surface of the glass fiber fabric with a knife afterapplying the second solution but before drying the applied secondsolution.
 9. The method of claim 1, wherein, after drying the appliedfirst solution, the second solution is applied to the first siliconerubber to apply the second silicone rubber such that the second siliconerubber is laminated on the first silicone rubber.